1. Field of the Invention
The invention generally relates to a fabrication method of an optical film, and more particularly to a fabrication method of a brightness enhancement film.
2. Description of Related Art
A liquid crystal panel of a liquid crystal display (LCD) does not emit light itself, so the LCD employs a backlight module behind the liquid crystal panel to provide light source. The liquid crystal panel decides the illumination fluxes of different positions on the liquid crystal panel, so as to generate displaying image for the viewer.
The backlight module provides a uniformity planar source for the LCD to display a displaying image having a good display quality. In order to increase the light efficiency of the LCD, the light beam generated by the backlight module may have a small lighting angle, so that the light beam may be effectively emitted on the liquid crystal panel and be used by the liquid crystal panel.
A brightness enhancement film (BEF) may decrease the divergence angle of the light beam generated by the backlight module. However, a normal BEF may converge the light beam in one direction, so that the backlight module may employ two BEFs to converge the light beam in two directions, and thus increase the thickness and the cost of the LCD.
A BEF having optical micro-structures on both of the upper surface and lower surface may solve the problems described above. For the optical micro-structures of both upper surface and lower surface may decrease the divergence angle of the light beam in two directions, the LCD may have a good light efficiency by employing one BEF having micro-structures on both of the upper surface and the lower surface. A method of fabricating the BEF having micro-structures on both of the upper surface and the lower surface includes forming two resin layers on both upper surface and lower surface of a light transmissive substrate, and rolling the two resin layers respectively with two rollers having micro-structures of the surfaces, so as to forming a plurality of first micro-structures and a plurality of second micro-structures respectively on the two resin layers. However, since error may be occurred when the two rollers are positioned or rolled, the BEF formed by the method may have the problems of low optical quality or low yield rate.